Her statement was released shortly after Donald trump made a live dress to the United States outlining the decision to launch airstrikes.
"This legally questionable action risks escalating further.an already devastating conflict".
British law does not require the government to seek parliamentary approval before going to war, but the country remains haunted by its lead role in Iraq.
Mr Corbyn, who has warned of an escalation in a "proxy war" between the U.S. and Russian Federation, said he would only consider backing intervention in Syria with the support of the United Nations.
May said intelligence and open source accounts indicated that the regime was behind the attack in Douma last Saturday.
She will repeat Saturday's assertion that Britain was "confident in our own assessment that the Syrian regime was highly likely responsible" and that it could not wait "to alleviate further humanitarian suffering caused by chemical weapons attacks", according to excerpts of her speech.
"The UK is permitted under global law, on an exceptional basis, to take measures in order to alleviate overwhelming humanitarian suffering", the statement said.
"The three leaders agreed that the military strikes taken against the Syrian Regime's chemical weapons sites had been a success", a No 10 spokesman said.
May seemed determined to resist calls for a retrospective vote on her actions, saying only that Parliament "will get an opportunity to question me" after she has made a statement on the attacks on Monday. It will be up to Speaker of the House of Commons John Bercow to decide whether to allow an emergency debate, and he has been a strong advocate of the right of Parliament to scrutinize the government.
On the suspected poison gas attack on Douma, Ms Haley said: "We know who did this".
Deploying the armed forces is a prerogative power, meaning the prime minister can launch action without backing from MPs.
Former Prime Minister David Cameron lost a parliamentary vote on air strikes against Mr Assad's forces in 2013 when 30 Conservative lawmakers voted against action, with many Britons wary of entering another conflict after intervention in Iraq, Afghanistan and Libya failed to bring stability to the region.
May recalled the ministers from their Easter holiday for the meeting at 3.30 pm (1430 GMT) in Downing Street to discuss Britain's response to what she has cast as a barbaric attack that can not go unchallenged.
The UK, United States and France launched "precision strikes" in Syria overnight.
Both Syria, which denies any chemical use, and Russian Federation, which provides military support to the Syrian government, have reacted angrily to the action. The strikes at 0100 GMT were 15 miles (24 kilometres) west of Homs.
"But the US administration is giving alarmingly contradictory signals", he said, calling for the government to press for an independent UN-led investigation of the chemical weapons attack in Syria. But British jets were scrambled as the cabinet met to discuss a response to the chemical attack.
"The position is a very risky one because of Russian involvement, also because we have an erratic president of the United States".
"It shows a weak government putting short term political expediency before democracy and in so doing further diminishing the standing of Britain in the world", Cable said.